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Softening surfaces stops liquids from splashing when they hit

A softer touch is called for

Markus Reugels/Getty

By Marcus Woo

Sometimes, you don’t want to make a splash – and now you don’t have to.

In a new experiment, physicists have shown how to stop droplets of liquid from flying through the air. By lining the lab bench or a surgeon’s instrument tray with soft materials, you can keep the splattering to a minimum.

“Even if you spill a couple of drops, you can be confident they are not going to splash,” says Alfonso Castrejon-Pita, a physicist at the University of Oxford. “The big drop is going to stay as a big drop, and that’s the end of the story.”

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Splashes are particularly problematic for those who work with hazardous chemicals or bodily fluids. When these liquids splatter, toxic or pathogenic droplets can become airborne.

Castrejon-Pita and his colleagues have now shown that when a drop of ethanol splatters off a hard acrylic surface, tiny jets form where the drop hits, disintegrating into smaller droplets. But when the researchers swapped the acrylic for soft silicone, the surface deformed upon impact, absorbing the energy from those jets. The jets don’t break away from the drop, and all that’s created is a puddle. To stop the splatter from a faster-falling drop, you just need an even softer surface.

Such splashless surfaces can have a variety of uses beyond labs and operating rooms, Castrejon-Pita says. They may help contain salmonella-infected raw chicken juices in kitchens, not to mention keeping toilets and urinals clean.

These results might also be relevant for the printing of electronic circuitry, which is akin to conventional inkjet printing. To speed things up, the printer has to fire the “ink” at higher speeds, which can splatter – but not if you print on soft materials like rubber. “That’s well aligned with the current technology trend, where you want flexible electronics,” he says.

Applications will probably take time, however. “This gives engineers a good guide to follow, but clearly more work is needed,” says Sigurdur Thoroddsen, a physicist at King Abdullah University of Science and Technology in Saudi Arabia. For example, researchers will have to explore the influence of other surface properties, such as roughness. And they will have to identify the materials most suitable for particular applications.

Still, the analysis provides important insight into the physics of a splash, such as the role of those tiny jets that form upon impact, and should spark lots of new research. “What’s exciting is it pinpoints where we should look for the origins of splashing,” Thoroddsen says. “It’s an important new discovery.”